Known energy transmission systems in the form of conductor line systems of the type known, for example, from DE 196 47 336 A1 feature devices that can be displaced on a conductor line, e.g., cable roller assemblies or transport suspension gears of an overhead conveyor. These devices frequently carry electrical loads such as driving motors for displacing the displaceable devices on the conductor line. In order to supply these electrical loads, current collectors with one or more sliding contacts are usually provided on one or more of the displaceable devices and can be inserted into corresponding voltage-carrying and current-carrying longitudinal line branches of the conductor line. In this case, the current collectors are rigidly connected to the displaceable devices and only the contacting of the sliding contacts with the line branches is realized in a movable fashion. Conductor lines of this type are normally used in manufacturing facilities that are accommodated in enclosed buildings. However, other types of conductor lines such as conductor rail systems or overhead contact systems known from railways may also be used for this purpose.
There is an increasing trend to also utilize conductor line systems in other systems with displaceable devices in order to supply electrical loads on the devices, for example, in cranes for loading containers or in RTG crane systems. In these systems, the loads arranged on the cranes are usually supplied via long lines that are wound onto and unwound from cable drums mounted on the cranes during a displacement. One example of such a cable drum arrangement is described in DE 44 29 268 A1. In order to displace the crane, the supply line is wound onto and unwound from the cable drum arranged on the crane in accordance with the movement of the loading crane. This known technique has the disadvantage that the line being wound and unwound needs to be placed on the ground without introducing significant tensile forces into the line. In addition, the line may become tangled while it is being wound or unwound such that the crane can no longer be displaced. In crane systems of this type with RTG cranes (Rubber Tired Gantry), the RTG cranes that are equipped with rubber tires and with a travel drive in the form of an internal combustion engine can be freely displaced in all directions. In the normal loading mode, the RTG cranes are positioned in longitudinal lanes between container loading berths and sort and load the containers in these loading berths. In order to quickly relocate containers in a full loading berth, RTG cranes are frequently pulled from currently empty or only slightly filled loading berths and driven to the full loading berth by means of the internal combustion engine. The electrical connection of the RTG cranes needs to be disconnected at the empty loading berth and reconnected at the full loading berth in a complicated, hazardous, and time-consuming fashion. In addition, the displacement of the RTG cranes by means of internal combustion engines is harmful to the environment and is becoming more and more expensive due to rising fuel prices, such that electric drives should be provided for movement within longitudinal lanes while the internal combustion engines should be used only for the free travel between the longitudinal lanes.
It would therefore be desirable, particularly in the field of crane systems, to supply the electrical loads on the crane with electric energy via a conductor line. However, since cranes of this type consist of very large systems that are typically used outdoors and therefore subjected to unfavorable ambient conditions, movements of the crane need to be decoupled as well as possible from movements of a current collector trolley that is connected to the crane and can be displaced on the conductor line.
One approach for this decoupling can be found in the field of rail-bound electric vehicles such as, for example, electric locomotives, in which one-leg pantographs or pantograph-type current collectors mounted on the roof of the locomotive usually can press a pantograph slipper against an overhead line. With respect to the supply of the vehicles with electric energy, it is particularly important that the pantograph slipper permanently contact the overhead line and this contact also be reliably maintained during motion-induced vibrations. The current collectors are therefore realized in such a way that a pressing mechanism reliably presses the pantograph slipper in the direction of the overhead line. This means that a force is continuously exerted in the direction of the overhead line.
One application of such pantograph-type current collectors in cranes is disclosed in DE 739 960 A. In this case, a double-link current collector is provided with a base plate, on which a skate is arranged by means of a double-link assembly with upper and lower link pairs in order to be guided along a conductor rail. The two lower links are connected to one another by means of a parallel motion such that their upper hinge points always carry out uniform motions, wherein the pressing force for the skate is generated by a tension spring that is arranged essentially parallel to the skate the between the upper links. An adjustment drive for retracting and extending the skate is not provided in this case.
Such a solution is very disadvantageous for conductor line current collector trolleys that are guided along a conductor line on a guide. In this case, a force needs to be continuously exerted transverse to the traveling direction, i.e., transverse to the longitudinal direction of the conductor line, such that the energy consumption increases. In addition, the constant pressing forces exerted transverse to the traveling direction leads to increased friction between the current collector trolley and the conductor line such that the energy consumption is additionally increased. Consequently, the displacement of the current collector trolley along the conductor line requires a significantly higher expenditure of force and energy. Since the current collector trolley is continuously pressed against the conductor line transverse to the traveling direction, the sensitive contacting between the sliding contacts and the longitudinal branches of the conductor line may become damaged. If the displaceable devices should be additionally displaced between several conductor lines at different locations as it is the case, e.g., with RTG cranes, damage may occur due to the protruding pantograph.